Generally, a vehicle is provided therein with seat belts, which restrain passengers as well as a driver for the sake of safety in crash, in order to attenuate deceleration exerted on a body of the passenger. The seat belt restrains the passengers during a collision. In addition to the seat belt, vehicles are provided with an airbag module rapidly inflating an airbag between a driver and a steering wheel or between a passenger in a passenger seat and an instrument panel in crash to attenuate the injury of the driver or the passenger caused by impact occurring in the crash.
FIG. 1 is a sectional view schematically showing an airbag module according to the related art, and FIG. 2 is a perspective view schematically showing a deployment shape of a passenger airbag module for a vehicle according to the related art. As shown in FIGS. 1 and 2, a passenger airbag module 100 for a vehicle includes an inflator 110, an airbag cushion 120, and a tether 130. The inflator 110 generates nitrogen gas (N2) upon explosion of a detonator. The airbag cushion 120 expands or deploys through a deployment part by nitrogen gas generated from the inflator 110. The tether 130 connects a front part of the airbag cushion 120, which makes contact with the body of the passenger, with a rear part 131a of the airbag cushion 120, into which nitrogen gas is injected from the inflator 110. The inflator 110 of the airbag module 100 includes a gas generating agent generating the N2 as the detonator of the inflator 110 is ignited, and the tether 130 is deployed by the nitrogen gas in a state in which the tether 130 is wound around the inflator 110.
In order to control deployment length of the airbag cushion 120, the airbag module 100 includes a rear part 131a coupling or fixing one end of the tether 130 to the rear part of the airbag cushion 120 and a front part 131b coupling or fixing the other end of the tether 130 to the front part of the airbag cushion 120. Regarding the operation of the airbag module 100 having the above structure, when the driving speed of the vehicle is abruptly decreased due to head-on crash, the impact sensor detects the impact occurring in the head-on crash and generates the impact signal. At this time, the electronic control module recognizes the impact signal, so the electronic control module ignites the detonator of the inflator 110 to burn a gas generating agent of the inflator 110, so that the gas generating agent generates the N2. While moving from gas exhaust ports 111 formed in the inflator 110 to a gas injection port 121 of the airbag cushion 120, the nitrogen gas expands or deploys the airbag cushion 120 toward the passenger.
The deployed airbag cushion 120 makes contact with the passenger to partially absorb impact. In addition, when the deployed airbag cushion 120 makes contact with the head or the chest of the passenger by inertia, the N2 of the airbag cushion 120 is rapidly exhausted through gas exhaust holes of the airbag cushion 120 to attenuate the impact exerted on the front part of the passenger. Accordingly, impact power applied to the passenger in the crash of the vehicle is effectively attenuated, so that a second collision, that is, a collision between other components of the vehicle and the body of the passenger can be reduced.
However, when the tether 130 wound around the inflator is deployed by the N2 inflating the airbag cushion 120, the tether 130 may not be linearly or progressively deployed toward the passenger, but may be spirally deployed or twisted due to the increase of the friction between the inflator and the tether. If the tether 130 is spirally deployed, the tether 130 may be twisted so that the deployment length of the airbag cushion is reduced, and the impact absorbing effect of the airbag cushion is reduced at the front of the passenger due to the reduction in deployment length of the airbag cushion. Accordingly, the airbag cushion may be abnormally or inconsistently deployed.